I had a weird experience yesterday as I was locking up my bike after my morning ride into the city.

Just as I'd finished locking it to a pole a very solidly built guy in a suit came up and commented "I wouldn't leave it there - someone might damage it".

As I was running late for a meeting I wasn't particularly inclined to debate my choice of parking spot with some random crazy man on the street - however he had the very direct manner of someone with a police or military background which had me particularly puzzled as to why he would care where my bike was parked.

I looked him in the eye and thanked him for his concern - he clocked that I was telling him politely to get lost and repeated his point, this time noting "I've seen people come up and stomp on the wheels and buckle them - its a nice bike and you shouldn't leave it there".

If he wasn't so obviously some sort of security guy I would have assumed he was a psycho looking to pick a fight, but I found myself unable to work out what his angle was so I thanked him again for his concern and then waited patiently for him to move on, which he did.

As I headed off to my meeting the best explanation I could come up with was that he was on his way to the law courts up the road and felt like being bossy, but it didn't feel very convincing.

A little later I could hear some noise coming from the street below the building I was in and looked out the window to see a tide of demonstrators moving down the road towards NSW state parliament. No one seemed to know what they were demonstrating about but their head-to-toe black clothing had most of the watchers (including me) guessing they were Muslims.

Before I moved away from the window I noticed that they were being particularly disciplined about staying together and had observers in high-vis jackets marching along each side of the column filming everything which seemed rather sophisticated for a protest march - most of them being fairly disorganised rabbles from my observations.

I spent the rest of the day trying to work out what Muslims would be protesting en-masse about. The afternoon news didn't mention anything about a march but did note NSW Parliament had voted down a same-sex marriage bill - but it was hard to imagine the local arm of the Taliban would be marching arm in arm with Alan Jones to oppose this.

Protesters wearing the white-faced Guy Fawkes masks that have become synonymous with the Occupy movement and the hacktivist grouping Anonymous have taken part in hundreds of gatherings around the world in opposition to causes ranging from corruption to fracking. Demonstrations in more than 400 cities had been planned as part of the event - billed as the "Million Mask March" - that coincided with Guy Fawkes Day.

One of the largest protests of Tuesday night took place in central London, where the comedian and advocate of "complete revolution" Russell Brand was pictured among crowds of people wearing a Guy Fawkes mask. "Whatever party they claim to represent in the day, at night they show their true colours and all go to the same party," said Brand on Twitter, using the #MillionMaskMarch hashtag. ...

In the US, protesters in Washington DC gathered at the Washington Monument before walking to the White House to raise awareness of causes including opposition to mass surveillance and genetically modified foods. Other protests, of varying size, took place in cities including Vancouver, Tel Aviv, Dublin, Paris, Chicago and Sydney. One of a number of Facebook pages for the event described it as a "Call for Anonymous, WikiLeaks, the Pirate Party, Occupy and Oath Keepers to defend humanity".

Needless to say, my bike was untouched when I emerged from the building later in the day...